1. Field of the Invention
The present invention relates to emergency communication links in a telephone network. In particular, the present invention relates to providing emergency services over a total IP (Internet Protocol) Telephone Network.
2. Description of the Related Art
Emergency calls, such as 911 calls, are currently placed over a telephone connection and routed to a Public Safety Answering Point (PSAP), where they are answered by attending personnel, such as a dispatcher. Emergency 911 calls are one of several X11-type calls (i.e. 911, 311, 511, etc.) that are handled at a PSAP. Usually, a TDM (Time Division Multiplex) connection to the telephone company's network connects the call to the PSAP. Time Division Multiplexing is a form of digital multiplexing in which two or more apparently simultaneous channels are derived from a given frequency spectrum (i.e., a bit stream) by interleaving pulses (representing bits) from different channels. In a TDM, a given channel is shared in time by two or more signals. The different signals alternate or take their turn in the channel.
IP Telephony, also called ‘Internet telephony’, is a technology that enables routing of voice conversations over the Internet or over a dedicated Internet Protocol (IP) network, instead of over dedicated voice transmission lines. Use of IP Telephony eliminates the use of circuit switching and the associated waste of bandwidth. Instead, packet switching is used, in which IP packets with voice data are sent over the network only when data needs to be sent, i.e., when a caller is talking. The protocols used to carry the signal over the IP network are commonly referred to as Voice over IP or VoIP protocols.
As VoIP technology gains in market acceptance, there is a need by the customers to utilize this technology for all types of services, including emergency services. In general, emergency services are not provided over a total VoIP network. Thus, when an IP telephone user dials 911, the call is directed to a vacant code (e.g., never finds a termination point, such as a PSAP). Those VoIP providers that do provide 911 service, such as the HIPCS (Hosted IP Communication Service) of SBC (Southwestern Bell Corporation), typically convert the VoIP call to TDM and redirect the call to the appropriate PSAP or call center over the TDM network. As VoIP service continues to expand, there is a need for providing a total VoIP network connection enabling X11 calls from a customer to a local PSAP or call center. The present invention addresses this need.